One of the first to apply the evolving physical philosophy of the Scientific revolution was a professor of science at Padua, Italy, named Santorio Santorio. His experiments laid the groundwork for the study of metabolism and the physical and chemical processes of the human body. Santorio also adapted the thermometer, invented by Galileo, to clinical purposes. Beginning in 1616, William Harvey, an Englishman who also studied at Padua, was the first to demonstrate, through dissection, that the circulation of blood through the human body is continuous. In coming to this conclusion, he broke with the beliefs of the ancient Greek physician, Galen, who assumed that the blood consisted of two types, one in the veins and the other in the arteries.
The contributions of Santorio and Harvey, combined with the advances in physics, gave impetus to the attempt to explain vital workings of the human body on mechanical grounds. The first book on physiology was written by Rene Descartes, who set forth a complex model of the animal structure. Many of his findings were later disproved, but at first his model attracted a significant following. Descartes also worked to determine the residence of human reason, or the soul. He claimed that he had discovered this in the pineal gland of the brain, which he wrongly believed to be unique to humans.
The Italian scholar Giovanni Alfonso Borelli was the foremost thinker of the era on human mechanics. His 1680 work, On the Motion of Animals, is widely recognized as the greatest early triumph of the application of mechanics to the human organism. Borelli, who extended his theories to touch upon the flight of birds and the swimming of fish, founded the modern study of muscular motion. Others attempted to explain human functions on the chemical level. Franciscus Sylvius introduced the idea of chemmical affinity to explain the human body's use of salts. He and his followers contributed greatly to the study of digestion and body fluids.
Advances were also made in the physical and chemical study of plants, largely spawned by Galileo's introduction of the microscope. Marcello Malpighi did much work with microscopes and conceived an erroneous model of plant circulation which, though incorrect, inspired further investigation into the subject. Malpighi also worked extensively with insects, and made significant advances in that field. Experimental work in the study of plants was done extensively by Edme Mariotte, who sought to explain sap pressure in plants by describing a mechanism by which plants permit the entrance but not the exit of liquid.
William Harvey's discovery that blood circulates through the human body was an important first step in the rejection of the physiology assumed by the students of Galen. The knowledge that the blood circulates was the foundation for an entire field of science that focuses on the importance of the blood. After Harvey's discoveries, curiosity quickly flared up regarding the questions of what exactly was carried by blood, where it was carried to and how dispensed. The study of the circulatory system has formed the cornerstone of animal biology since Harvey's time, each generation achieving a more complete understanding of some aspect or other of the system, or the function of some organ or other which is touched by it.
The advances made in physics led many biologists to see the human body as a conglomeration of separate mechanisms, relying on the laws of physics to function, with joints as fulcrums using the principles of leverage and all body parts subject to the same laws which governed mechanisms built out of wood or metal. This emphasis on separating the various functions of the human body into separate parts often had the negative result of causing biologists to lose sight of the larger picture of the body in total, which though a physicist might explain the operation of each of its individual parts, remains something of a mystery as a complete organism. Similarly, Descartes attempted to discern the location and properties of the mechanism which produces the human quality of reason and will. Though the pineal gland has since been proven to be not unique to humans, and the inhabitants of modern times might scoff at Descartes presumption, the source of human reason and will remains unknown, and the full process of translating thoughts into actions is not understood. Descartes' theory demonstrates the zeal of attempted mechanization of the human body, but in reality, his hypothesis is no more flawed than many which have been presented since.
The intensified study of biology during the seventeenth century revived the spirit of inquiry into nature produced by the Renaissance and resumed the questioning of the traditional explanations of the Aristotelian system. Though many of the claims of the Aristotelian system, especially in regard to animal biology, were eventually proven correct, many of the ancient truths of biology, both animal and plant, broke down during the seventeenth century. Chemical studies of the human body began to break down the medieval belief that the human body was filled with four substances, or 'humors'--blood, yellow bile, black bile, and phlegm--which if thrown out of balance caused illness. Edme Mariotte took steps toward the rejection of the Aristotelian beliefs surrounding plant biology by questioning the ancient belief in a vegetative soul. Mariotte demonstrated that every species of plant, and even the parts of a plant, exactly reproduce their own properties in their offspring. He affirmed that all of the vital processes of plants were the result of the interplay of physical forces and denounced any non-mechanical explanation.